Hypothesis that the Earth was entirely frozen over on 3 separate occasions (Marinoan, Sturtian, Kaigas) during the Cryogenian period (850-630 million years ago).

Evidence for the hypothesis comes from world glacial rock formations which date to the Cryogenian period.

Embryo Of An Idea By Mikhail Budyko:

Mikhail Budyko, a Russian climatologist, in the 1960s developed a climate model to investigate the effect of ice cover on global climate.

Budyko's results suggested that if ice sheets advanced far enough out of the polar regions a feedback ensued where the increased reflectiveness (albedo) of the ice led to further cooling & the formation of more ice.

Eventually the the entire Earth could be covered in ice and stabilized in a new ice-covered equilibrium.

Budyko (1969) concluded that this event could never happened, because his model suggested no way to escape from the simulated outcome. [1]

Snowball Earth Hypothesis Is Born:

"Snowball Earth" was first coined by Joseph Kirschvink (professor of geobiology at the California Institute of Technology) in 1992.[2]

The hypothesis was originally considered to help explain the apparent presence of glaciers at tropical latitudes.[3]

How did the Earth thaw out?

A recent report suggests that the Earth may have been more mudball than snowball.

It was hypothesised that CO2 levels may have risen during the snowball period, leading to a thaw in the Earth, though CO2 levels seem to have been too low for this.

Recent research suggests that areas with a higher level of volcanic dust or weathered rock, may have been able to absorb sunlight enough to cause a rewarming.[1]

Snowball Earth Relationship To Evolution:

Organism size & complexity increased markedly after the end of the Snowball Earth glaciations.

Evolutionary pressures may have been increased by "icehouse-hothouse" cycles, leading to multicellular organism development.

Fluctuations in nutrient levels and oxygen may have contributed to evolutionary selective pressures.

It is hypothesised that kin selection (with organ-like differentiation) may have been a driver for more complex life; this occurring at the expense of individual cell reproduction.

The evolutionary pressure producing high relatedness (i.e. kin selection) associated with glaciations may have helped overcome the reproductive cost of forming a complex animal.